1. Field of the Invention
The present invention relates to a method for transferring impact energy from a top hammer unit to a bore, which unit gives compressive pulses with a longitudinal direction. The tool comprises an intermediate portion cooperating with a drill bit. The drill bit comprises a shank with a first length as well as a bit head with a second length and provided with crushing means. A bit portion, such as a shoulder or a blind hole, is provided in connection with the bit head, said bit portion having a first abutment surface facing towards the free end of the intermediate portion. The free end of the intermediate portion is provided with a second abutment surface, facing towards the drill bit. The top hammer unit is brought to transfer compressive pulses to the intermediate portion, wherein each compressive pulse is transferred to the drill bit via the impact surfaces. The intermediate portion and the drill bit comprise cooperating devices for driving and retaining. The invention further relates to a drill bit and a drilling tool for drilling with the aid of a top hammer unit, a drill bit as well as an intermediate portion.
2. Description of the Related Art
Through U.S. Pat. No. 4,619,334 is previously known a jointed connection for percussive drilling, said connection comprising an element which connects, relatively each other movable, tube ends. At compressive pulses, the tube ends are brought to abutment against each other while they are separated at tensile pulses. There are several problems with inlaid elements in a drill string for percussive drilling. Elements can easily break during use to the great forces which are used at the drilling. The drill string furthermore becomes complicated and troublesome to mount. A drill bit is shown as a preferred embodiment in said patent, wherein the head of the drill bit has a considerably larger impedance than the impedance of the drill bit shank. This means that the impact between the tube and the bit, a compressive pulse will be reflected upwardly back to the tube, which reflection is proportional to the difference in impedance between the cooperative parts. This reflection of pulses implies a high temperature and a high level of sound, increased wear and impaired efficiency.